The potential effects of a galactic null wave would be global dimming, cooling and a drop in active weather circulation. These circumstances would elicit the same effect on individuals.

It would also manifest in the alteration of tonal characteristics to a more bass droning character.

Any of these seem familiar?

Lethargy, headaches, a constant perturbation or vibrating feeling. Higher incidence of seeming time interruption, blips, deja vu's, synchronicities?

think of it as the athmosphere about you getting thicker. More pressure, less action or dynamism. Any actions will cause higher displacement but to less of an area of effect.